JP7116042B2 - Devices, systems and methods for monitoring peripheral arterial perfusion in a subject - Google Patents

Description

The present invention relates to processing devices, systems and methods for monitoring peripheral arterial perfusion in a subject.

Perfusion is a common hemodynamic aspect that needs to be measured in critically ill patients. Photoplethysmography (PPG) is a known technique that can be used to monitor perfusion. PPG is an optical measurement technique that evaluates the change in light reflectance or light transmission of an area or volume of interest over time. Since PPG is based on the principle that blood absorbs light (more than the surrounding tissue), variations in blood volume with each heartbeat affect transmittance or reflectance accordingly. In addition to information about heart rate, the PPG waveform can contain information due to additional physiological phenomena such as respiration. By evaluating the transmittance and/or reflectance at different wavelengths (typically red and infrared), blood oxygen saturation can be determined.

Discreet vital signs monitoring using video cameras or remote PPGs has been demonstrated and discovered in the context of patient monitoring. Remote PPG imaging is described, for example, in Non-Patent Document 1. It is based on the principle that temporal variations in blood volume in the skin lead to variations in light absorption by the skin. Such variations can be recorded by a video camera taking images of skin areas, for example the face, while processing computes pixel averages over a selected area (typically the cheek area in this system). do. By looking at the periodic variation of this average signal, the heart rate and respiration rate can be extracted. Meanwhile, there are several additional publications and patent applications detailing devices, systems and methods for obtaining patient vital signs through the use of remote PPG.

Arterial blood pulsation thus causes a change in light absorption. These changes observed on a photodetector (or an array of photodetectors) form a PPG (photoplethysmography) signal (also called plethysmography among others). The blood pulse is caused by the heartbeat, ie the peaks of the PPG signal correspond to the individual beats of the heart. Thus, the PPG signal is itself a heartbeat signal. The normalized amplitude of this signal varies with wavelength and is also a function of blood oxygenation for some wavelengths.

WO 2005/020003 and WO 2004/020002 disclose systems and methods for measuring one or more light absorption-related blood analyte concentration parameters of a mammalian subject. The system comprises: a) a photoplethysmography (PPG) device configured to perform PPG measurements by illuminating the skin of a subject with at least two distinct wavelengths of light and determining the relative absorbance of each wavelength and b) a dynamic light scattering (DLS) device configured to perform dynamic light scattering (DLS) measurements of a subject to rheologically measure pulse parameters of the subject. c) i) temporally correlating the results of the PPG and DLS measurements, and ii) values of one or more light absorption-related blood analyte concentration parameters according to the temporal correlation between the PPG and DLS measurements; an electronic circuit configured to evaluate the

(2001) mentions the use of a laser speckle detector for remote optical determination of cardiovascular health. A conventional PPG device is used as a reliable reference for measuring the signal obtained using a laser speckle detector.

[3] mentions a comparison between photoplethysmography (PPG) and laser Doppler flowmetry (LDF).

US Pat. No. 5,300,000 discloses a wearable pulse oximetry device that is mounted on a wrist band and anchors the area above the tip of the ulna with a dome-shaped structure. This area is used as the measurement area. Measurements are made with a detector positioned above the immobilization area. A detector detects light emitted by light sources of different wavelengths located around the fixed area. Reflection is therefore measured neither in reflection mode nor in transmission mode, but at angles between 20° and 60° from the emitted light. This mode, called trans-illumination mode, makes it possible to achieve excellent signal-to-noise ratios and enables continuous and reliable measurement of wrist oximetry data. It is further described that coherent light scattering (CLS) can be used to combat motion artifacts.

If the PPG signal is low, there are two possible scenarios:
i) The patient is centralized or suffers from vascular sclerosis. The vessels are relatively stiff (high arteriolar and venular tone resulting in high vascular resistance) and have a low response to fluctuations in blood volume during the cardiac cycle. This has to do with the inability of the vessel wall to respond to the heartbeat, which induces pulsatile pressure/flow fluctuations. Therefore, vascular compliance, ie the ability to dilate upon arrival of a blood pressure pulse, is low.
ii) low cardiac output; In this case the weakness of the PPG signal is caused by low blood volume in the heartbeat.

Therefore, PPG monitoring of peripheral perfusion distinguishes between hypopulsatility caused by low vascular compliance (due to centralization and/or vascular stiffness) and hypopulsatility caused by low cardiac output. Can not do it.

U.S. Patent Application Publication No. 2015/0105638 U.S. Patent Application Publication No. 2011/0082355 International Publication No. 2013/030744 pamphlet

Wim Verkruysse, Lars O. Svaasand and J. Stuart Nelson, "Remote plethysmographic imaging using ambient light," Optics Express, Vol. 16, No. 26, December 2008 Farley et al., “Optical determination of cardiovascular health at a distance,” proceedings of the International Society for Optical Engineering (SPIE), vol. 7703, 77030R, 2010 Lindberg et al., “Photoplethysmography, Part 1: Comparison with laser Doppler flowmetry,” Medical and Biological Engineering and Computing, vol. 29, No. 1, p. 40-47, 1991 Briers, "Laser Doppler and time-varying speckle: a reconciliation", the Journal of the Optical Society of America, vol. 13, no. 2, 1996 Briers, “Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging”, physiol. Meas. 22, R35-R66, 2001

It is an object of the present invention to provide a process for use in monitoring peripheral arterial perfusion in a subject that allows to distinguish between hypopulsatility caused by low vascular compliance and hypopulsatility caused by low cardiac output. It is to provide a device, system and method. In particular, a process for use in monitoring peripheral arterial perfusion in a subject that supports differentiation between well-compensated hypovolemia and ill-compensated hypovolemia. It would be advantageous to provide devices, systems and methods.

In a first aspect of the invention, a processing device is presented for use in monitoring peripheral arterial perfusion in a subject. Such processing devices are:
- an input for receiving first detected data of a tissue region of the subject and for receiving second detected data of a skin region of the subject, wherein the first detected data are reflected from tissue of the subject; and/or obtained over time by detecting radiation transmitted through tissue of the subject, the second detection data detecting radiation received from the skin area in response to coherent light emitted toward the skin area. an input obtained over time by;
a PPG unit for deriving a photoplethysmography (PPG) signal from the first detected data;
a flow unit for deriving from the second detection data a flow signal indicative of the flow of light scattering particles within the skin area;
An evaluation unit for evaluating the PPG signal and the flow signal to obtain information about peripheral arterial perfusion, the evaluation unit being based on a combined evaluation of the PPG signal and the flow signal to determine low vascular compliance. an evaluation unit adapted to determine a condition (e.g. a centralized vascular condition and/or a condition of low cardiac output;
Prepare.

Additionally or alternatively, the evaluation unit may be configured to evaluate the PPG signal and the flow signal to obtain information on peripheral arterial perfusion, wherein the evaluation unit is adapted to determine a centralized vascular condition or a condition of low cardiac output based on a combined evaluation of .

In a further aspect of the invention, a system for monitoring peripheral arterial perfusion in a subject is presented. The system will:
- a detector for obtaining first detected data of a tissue region of the subject and second detected data of a skin region of the subject, the first detected data being reflected from the tissue of the subject; and/or a detector obtained over time by detecting radiation transmitted through the tissue of the subject, the second detection data comprising a series of images of the skin area obtained over time;
- a processing device disclosed herein for monitoring peripheral arterial perfusion based on acquired first and second sensing data;
Prepare.

In yet a further aspect of the invention, a corresponding method, a computer program comprising program code means for causing a computer to perform the steps of the methods disclosed herein when the computer program is executed on a computer, as well as a processor Also provided is a non-transitory computer-readable recording medium storing a computer program product that, when executed by, causes the methods disclosed herein to be performed.

Preferred embodiments of the invention are defined in the dependent claims. The claimed methods, systems, computer programs and media are defined in particular in the dependent claims and have preferred embodiments similar and/or identical to those disclosed herein as claimed Please understand.

The present invention is based on the idea of alleviating the above ambiguity regarding hypopulsatility. laser speckle imaging or laser obtained from a flow signal (e.g. speckle signal or laser Doppler signal) indicative of the flow of light scattering particles in a skin region (preferably identical to the tissue region), especially in addition to the PPG signal Information about peripheral arterial perfusion can be obtained based on interferometric techniques such as Doppler. Vascular compliance is low, especially when the flow signal indicates high flow velocities and the PPG signal measures relatively low blood volume fluctuations. In other words, blood vessels are not responding well to increased blood flow. A similar conclusion can be drawn that normal or high vascular compliance results in increased blood volume (measured by the PPG signal) resulting in higher blood flow velocities (which can be measured by speckle or laser Doppler signals). should prevent

Generally, the first detection data and the second detection data are obtained separately (ie, received or retrieved from the detector or database). For example, a detector (eg, PPG sensor) can be used to obtain first detected data, and an imaging unit (eg, camera) can be used to obtain second detected data. However, in one embodiment, the second detection data is used as the first detection data, i.e. the first detection data is identical to the second detection data, and the detector acquires image data representative of the second detection data. This is an imaging unit for

As used herein, perfusion refers to how much blood flows through a given tissue area, ie units of blood volume per time per tissue volume. Thus, perfusion can be high even in the absence of pulsatile blood volume or pulsatile blood flow, ie, with completely non-pulsatile flow. Vice versa, for example, with blood flow occlusion but with hyperpulsatile input, a strong PPG signal is seen even with hypoperfusion. Thus, as used herein, a (pulsatile) PPG signal is an absorption-dominant signal resulting from a pulsatile blood volume, ie indicative of the absorption of light within a tissue region. The (pulsatile) flow signal, on the other hand, results from the (pulsatile) movement of particles within the tissue region. Speckle patterns can be disturbed or frequency shifts can occur, for example due to moving particles. The flow signal can be determined using the principles of laser Doppler or laser speckle imaging (LSI). Therefore, the PPG and flow signals can be described as color-based probing of blood absorption and color-blind probing of blood motion, respectively.

As used herein, a PPG signal can be considered a conventional PPG signal that indicates the absorption of light within a tissue region at a given wavelength.

As used herein, flow signals can be acquired by techniques such as Laser Speckle Imaging (LSI) or Laser Doppler. Coherent (laser) light scattered from a moving object or particle produces intensity fluctuations that can be used to measure the velocity of the scatterer. An overview of laser Doppler and speckle is given in Briers, Ref. 4 and Briers' review report on the topic, Ref. A flow signal can indicate the extent to which light received from a subject's skin area is disturbed by moving particles, such as blood cells. In short, laser Doppler velocimeters use the frequency shift caused by the Doppler effect to measure velocity. It can be used to monitor blood flow in the body. Laser speckle refers to a random interference effect that gives an object illuminated by laser light a grainy appearance. If the object contains individual moving scatterers (such as blood cells), the speckle pattern will vary.

Low vascular compliance is subdivided into or attributed to two distinct conditions: (i) vascular stiffness and (ii) centralized condition. Vascular stiffness can refer to the stiffness/elasticity of the vessel wall, which can change, for example, with age and with cardiovascular disease. A centralized state means that the body increases vascular tone (reduces diameter) in the arteries of peripheral tissues (arms and legs), reducing blood flow to these peripheral tissues and allowing more blood flow. It may refer to a compensatory cardiovascular state that seeks to target central organs. Although vascular stiffness changes very slowly over time, typically on the order of years, concentration can occur within seconds/minutes. Both increased stiffness and vascular tone result in decreased vascular compliance (the ability to dilate upon arrival of a blood pressure pulse). The solution proposed here makes it possible to investigate the vascular compliance of arteries within the tissue under study by evaluation of the combined PPG and flow signals. Interpretation of changes in vascular compliance, whether they are due to changes in vascular stiffness or changes in vascular tone, is highly dependent on the timescale on which the changes occur. Thus, as used herein, the term vascular compliance can encompass both (age-related) vascular stiffness and centralization.

In a further refinement, the evaluation unit is adapted to determine the status of good decompensated hypovolemia and poor decompensated hypovolemia based on a combined evaluation of the PPG signal and the flow signal.

For example, conditions of low cardiac output can lead to localization causing vasoconstriction of peripheral tissues. Vasoconstriction reduces vessel diameter and compliance. Although the blood vessels stiffen due to this, vascular compliance is reduced because this is caused by the smooth muscle surrounding the artery rather than the arterial wall (i.e., not age-related stiffening due to arteriosclerosis). When a patient becomes hypovolemic (i.e., when the patient loses blood volume), the body concentrates to redirect flow to the heart to maintain cardiac output, even though blood volume is low. The flow remains unchanged, but the PPG signal is expected to decrease first. As a second step, when the body is no longer able to compensate/focus, cardiac output and flow signal may also drop. Evaluation of the combination thus makes it possible to distinguish between well-compensated and uncompensated hypovolemia. Advantageously, the evaluation unit evaluates the PPG signal and the flow signal over time and, based on the temporal behavior of the PPG signal and the flow signal, in particular changes in vascular compliance (PPG vs. LSI) and flow (LSI). By evaluating the PPG signal and the flow signal, it is possible to distinguish between good and poor decompensated hypovolemia.

According to an embodiment, the evaluation unit is arranged to evaluate the speckle pattern represented by the flow signal (in this case representing the speckle signal). When a diffuse medium is illuminated, the interference creates a speckle pattern. If there is motion in the medium, this causes motion blur of the speckle pattern, which can be used to extract information about the motion. This is evaluated according to the present embodiment.

Thereby, the evaluation unit is preferably arranged to evaluate motion blur by detecting variations in speckle contrast.

According to another embodiment, the evaluation unit is configured to evaluate the PPG ratio of the AC component to the DC component of the PPG signal and the speckle ratio of the AC component to the DC component of the flow signal. The PPG signal is composed of a pulsatile waveform (AC component) caused by changes in blood volume with each heart beat superimposed on a lower frequency, slowly varying DC component caused by respiration and movement. By analogy with the PPG signal, the blood flow signal can be decomposed into an AC component reflecting the modulation of blood flow velocity and a DC component reflecting blood flow. Combining the two signals allows distinguishing poor peripheral perfusion from low cardiac output.

The evaluation unit advantageously determines a state of good compensated hypovolemia in the subject if the speckle ratio exceeds a first speckle threshold and the PPG ratio is below a first PPG threshold, the speckle ratio configured to determine decompensated hypovolemia in the subject if less than the 2 speckle threshold and the PPG ratio is less than the first PPG threshold.

In another embodiment, the evaluation unit determines non-compliant blood vessels (and high peripheral perfusion) if the speckle ratio exceeds a second speckle threshold and the PPG ratio exceeds a second PPG threshold. and if the speckle ratio is less than the second speckle threshold and the PPG ratio is greater than the second PPG threshold, determine the condition of compliant blood vessels. As noted above, vascular compliance indicates the ability to dilate upon arrival of a blood pressure pulse. A (too) high flow rate in combination with a PPG ratio above the second PPG threshold may indicate that the vessel is poorly adapted to the arrival of the blood pressure pulse and is therefore non-compliant (or poorly adapted). (not shown) may indicate blood vessels. A respective threshold may for example be predetermined and may be obtained from previous measurements, eg as an average of measurements of a plurality of subjects or from previous measurements of the same subject. The threshold may be adaptive, eg, adjusted from time to time based on measurements of the same subject, as a sort of learning system.

によって与えられる、スペックル比に対するＰＰＧ比の比を示すコンプライアンス測定値Ｐを評価するように構成され得る。ここで、スペックル比は、フロー信号のＤＣ成分に対するＡＣ成分の比であり、ＰＰＧ比は、ＰＰＧ信号のＤＣ成分に対するＡＣ成分の比である。Pの増加は血管コンプライアンスの増加を示すことができる。ＤＣ流における減少を伴うPの減少は心拍出量の減少を示すことができる。 Optionally, the evaluation unit provides perfusion measurements, more precisely

may be configured to evaluate a compliance measure P that indicates the ratio of the PPG ratio to the speckle ratio given by: Here, the speckle ratio is the ratio of the AC component to the DC component of the flow signal, and the PPG ratio is the ratio of the AC component to the DC component of the PPG signal. An increase in P can indicate an increase in vascular compliance. A decrease in P with a decrease in DC current can indicate a decrease in cardiac output.

The input unit is configured to obtain first detection data obtained in response to artificial illumination of the tissue region with predetermined radiation, in particular with visible or infrared light. For this purpose, the system may comprise an illumination unit for artificial illumination of tissue areas with predetermined radiation, in particular with visible or infrared light. For example, one or more LEDs can be used as illumination units, such as those conventionally used in PPG imaging. A laser device for emitting a laser beam for illuminating the skin area may alternatively or additionally be used to obtain the second detection data from which the flow signal is derived.

Preferably, in one embodiment, a single lighting unit is used to illuminate the skin area, and thus the skin area from which PPG data is derived (although this is generally preferred, but not essential). Only a single set of second sensed data is obtained, corresponding to the tissue region in which the flow signal and the PPG signal are derived, from the second sensed data.

In one embodiment, the flow unit may be configured to derive flow signals based on laser Doppler and/or laser speckle techniques. According to the Doppler principle, light that hits a moving particle such as a blood cell undergoes a wavelength/frequency change (also called Doppler shift), while a light particle that encounters a static structure returns unchanged. A portion of the light can be registered by a detector such as a photodiode. Since the magnitude and frequency distribution of Doppler-shifted light are directly related to the number and velocity of blood cells, a flow signal can be calculated based on the detected data. The output signal can thus provide information about microcirculatory blood flow at the first and second wavelengths. For further details, see the aforementioned publication by Briers on basic principles of laser Doppler and laser speckle techniques.

These and other aspects of the invention will become apparent and explained in connection with the embodiments described below.
1 is a schematic diagram of a first embodiment of a system according to the invention; FIG. 1 is a schematic diagram of a first embodiment of a device according to the invention; FIG. Fig. 4 is a schematic diagram of a second embodiment of the system according to the invention; FIG. 2 illustrates AC and DC components of a PPG signal; FIG. 11 shows a low-modulation PPG signal and a low-modulation speckle signal; FIG. 11 shows a low-modulation PPG signal and a high-modulation speckle signal; Fig. 3 shows a flow chart of the method according to the invention;

FIG. 1 shows a schematic diagram of a first embodiment of a system 10 and processing device 12 for monitoring peripheral arterial perfusion of a subject 14 according to the present invention. The processing device 12 may be abbreviated as the device 12 below. A subject 14, in this example a patient, may be lying in bed 16, for example in a hospital or other medical facility, but may be a newborn or premature infant, for example lying in an incubator, or a person at home or in another environment. may be

In addition to the device 12, the system 10 acquires first detected data of a tissue region 13 (eg, forehead, cheeks, hands, etc.) of the subject 14 and a skin region 15 (eg, forehead, cheeks, hands, etc.) of the subject 14. , i.e. the same area as the tissue area or a different area). First detected data is obtained over time by detecting radiation reflected from and/or transmitted through tissue of subject 14 . The second sensed data includes a series of images of the skin area acquired over time. Based on the acquired first sensed data and second sensed data, device 12 determines peripheral arterial perfusion of subject 14 .

There are different embodiments of detectors (also called signal acquisition units) for detecting electromagnetic radiation transmitted through or reflected from a subject and acquiring second detected data. Different embodiments are used together in the embodiment of system 10 illustrated in FIG.

In order to obtain second detection data of the subject 14 from the skin area 15 , the detector is adapted, in particular, to capture (remotely and unobtrusively) image frames of the subject 14 . A camera 18 (also called an imaging unit) containing a suitable photosensor is provided to acquire image frames of . The image frames captured by camera 18 may correspond in particular to a video sequence captured by, for example, an analog or digital photosensor in a (digital) camera. Such cameras 18 typically include photosensors, such as CMOS or CCD sensors, which can operate in a particular spectral range (visible, IR) or can provide information on different spectral ranges. Camera 18 may provide analog or digital signals. An image frame includes a plurality of image pixels having associated pixel values. In particular, an image frame includes pixels representing light intensity values captured at different photosensitive elements of the photosensor. These photosensitive elements can be sensitive in a particular spectral range (ie, exhibit a particular color). An image frame includes at least two groups of several image pixels, each representing a different skin region of the subject, such as forehead, cheeks, throat, hands, and the like. Thus, an image pixel may correspond to one photosensitive element of the photodetector and its (analog or digital) output, or may be determined based on a combination (e.g., by binning) of multiple photosensitive elements. good.

To obtain first detected data of the tissue region 13 of the subject 14 , the detector is configured to attach to the tissue region 13 of the subject 14 to obtain photoplethysmographic signals from the tissue region 13 . A photoplethysmographic sensor 19 (also called a contact PPG sensor) is provided. The PPG sensor 19 may be a finger clip (as conventionally used to measure blood oxygen saturation) or may be designed in the form of a sticker). The PPG sensor 19 may be designed in other forms and may be placed on other skin areas of the subject's body.

System 10 optionally includes light source 22 (illumination source 22), such as a lamp or laser, for example, to illuminate tissue region 13 in one or more predetermined wavelength ranges (eg, red, green and/or infrared wavelength ranges). ) can also be included. The light source 22 particularly comprises a coherent light source for emitting coherent light, particularly at a predetermined wavelength or wavelength range. Light reflected from tissue area 13 in response to that illumination is detected by camera 18 . In another embodiment, no dedicated light source is provided, but ambient light is used to illuminate the subject 14 . From the reflected light, a desired wavelength range of light (e.g. green, red and/or infrared light, or a sufficiently large wavelength range to cover at least two wavelength channels) can be detected and/or evaluated. can.

Device 12 preferably provides an interface for medical personnel to display the determined information and/or change settings of device 12 , camera 18 , PPG sensor 19 , light source 22 and/or any other parameters of system 10 . is further connected to the interface 20 to provide a Such interfaces 20 may include different displays, buttons, touch screens, keyboards or other human-machine interface means.

A system 10 as illustrated in FIG. 1 may be located, for example, in a hospital, medical facility, aged care facility, or the like. Apart from patient monitoring, the present invention finds application in other fields such as neonatal monitoring, general surveillance applications, security monitoring, or so-called lifestyle environments, such as fitness equipment, wearables, handheld devices such as smartphones, etc. may also apply. One-way or two-way communication between device 12, camera 18, PPG sensor 19 and interface 20 may operate via wireless or wired communication interfaces. Other embodiments of the present invention may include device 12 integrated into camera 18 or interface 20, but not provided standalone.

Figure 2 shows a schematic diagram of a first embodiment of a device 12a according to the invention. Device 12a may be used as device 12 in system 10 illustrated in FIG. The device 12a comprises an input (or input interface) 30 for acquiring (ie, retrieving or receiving) first sensed data of tissue regions of the subject and second sensed data of skin regions of the subject. The first sensed data is acquired over time by detecting radiation reflected from and/or transmitted through the tissue of the subject, and the second sensed data is acquired over time of the area of skin. Contains a series of images.

Device 12a further includes a PPG unit 32 for deriving a PPG signal from the first sensed data and a flow unit 34 for deriving a flow signal from the second sensed data, the flow signal being the light scattering within the skin region. Particle flow is shown. The flow signal may be, for example, a speckle signal representing speckle or a Doppler signal representing Doppler shift. Evaluation unit 36 evaluates the PPG signal and the flow signal to obtain information regarding peripheral arterial perfusion of subject 14 . Advantageously, the evaluation unit 36 is adapted to determine (or distinguish between) a state of low vascular compliance and/or a state of low cardiac output based on a combined evaluation of the PPG signal and the flow signal. be done. In other words, the evaluation unit may be adapted to classify the subject's condition as a condition of low vascular compliance and/or a condition of low cardiac output based on the combined evaluation of the PPG signal and the flow signal. . PPG unit 32, flow unit 34 and evaluation unit 36 may be implemented in hardware and/or software, for example by one or more programmed processors or computers.

FIG. 3 shows a schematic diagram of a second embodiment of a system 10a according to the invention. Unlike the first embodiment of system 10 illustrated in FIG. 1, system 10a comprises only a single detector 18, ie camera (or imaging unit). Therefore, the second sensed data acquired by camera 18 is also used as the first sensed data for deriving the PPG signal using the remote PPG technique described above. Hence, no additional PPG sensor (19 in FIG. 1) is required and the tissue area therefore corresponds to the skin area.

Further details and further embodiments of the invention are described below.

PPG monitoring of peripheral perfusion cannot distinguish between hypopulsatility caused by low vascular compliance (centralization and/or vascular stiffness) and hypopulsatility caused by low cardiac output. Considering blood vessels, the heartbeat induces pulsatile pressure/flow fluctuations. The following analysis considers sinusoidal pressure fluctuations for illustration purposes:
Δp = Δp ₀ cosωt (1)
where Δp ₀ is the pressure constant and ω is the heartbeat frequency.
In response to this external stimulus, the vessel walls dilate or contract to allow more or less blood volume to circulate.

Blood pulsatility can be measured from the PPG signal. PPG is a technique that measures changes in blood volume in the microvascular bed of tissue caused by blood pressure fluctuations. This is an optical technique and measures light absorption over time. The PPG signal consists of a pulsatile (AC) waveform caused by changes in blood volume with each heartbeat superimposed on lower frequency, slowly varying (DC) components caused by respiration and movement. As illustrated in FIGS. 1 and 3, this technique can be applied both contact-based (cPPG) using contact-source/detector geometry and remote-based (rPPG) using a camera.

The fluid flow rate q, by definition, is the volume of fluid passing near the same location through an area in a given period of time and can be expressed as:
q = vA (2)
where A is the cross-sectional area of the tubular shape and v is the average velocity of the fluid over that area, both taken at the location where the flow rate is measured. From fluid mechanics, given a flow through a tubular geometry, the following relationships between the external pressure Δp, the fluid flow q, the fluid volume ∫qdt and the flow variation dq/dt and the inherent mechanical properties of the tubular geometry can be established:
∫qdt＝CΔp (3)
q=Δp/R (4)
dq/dt = Δp/L (5)
where L is the inductance, R is the vascular resistance, and C is the vascular compliance related to the elasticity of the vessel wall.

ここで、外力は、式（１）による心臓周期中の血圧の変動である。 Therefore, the flow fluctuations caused by pulsatility can be expressed as a solution to a differential equation:

where the external force is the variation in blood pressure during the cardiac cycle according to equation (1).

The PPG signal correlates with blood volume in the tissue. Therefore, when it is low, according to the compliance relationship (equation 3), when the pulsatile component of the PPG signal is low, it corresponds to a small depth of PPG signal modulation AC/DC, which can be interpreted in two ways. We can conclude that:
i) Low C: Low compliance. e.g. vascular sclerosis;
ii) Δp is low: blood flow is stable at low cardiac output; this means that R _q is low and therefore either blood flow q or blood flow velocity v is low.

Thus, in this case, the PPG method is ambiguous in distinguishing between poor peripheral perfusion (eg, low compliance due to vascular stiffness or centralization) and low cardiac output.

The proposed device, system and method alleviate this ambiguity. Low peripheral perfusion is associated with either low cardiac output or low vascular complianceC. When there is low cardiac output, blood flow q is low according to the vascular resistance relationship Δp=R _q between blood flow and pressure fluctuations. In other words, if a high vascular flow q is observed when the PPG signal is low, it cannot be caused by low cardiac output. Rather, the vessel wall does not respond to blood pressure by changing its volume (hence low vascular compliance), but by changing blood flow velocity.

ここで、A＝πr²及び式（２）が使用される。 In the following, equations from fluid dynamics are used to establish the relationship between the measured signal, blood volume and blood flow. Combining the formula for vascular resistance R for laminar flow (Hagen-Poiseuille formula):
R=8ηL/ ^πr4 (7)
and the flow depends on the resistance (equation 4) and the compliance (equation 3), where R is the resistance to blood flow, L is the length of the vessel, η is the viscosity of the blood, r is the radius of the vessel, Where q is blood flow and C is vascular compliance, the following relationship can be derived:

where A=πr ² and equation (2) are used.

であるか、同等に、

であり、これは、図４に図示されるように、ＰＰＧ信号変調深さ（ＰＰＧ信号のＡＣ／ＤＣ成分）に相関される。 Therefore, when vascular compliance is very low, i.e. C → 0, then:

or, equivalently,

, which is correlated to the PPG signal modulation depth (the AC/DC components of the PPG signal) as illustrated in FIG.

明らかに、1/v dv/dtを測定することは、以下のようにあいまいさを軽減することができる。すなわち、1/v dv/dtが低い場合、次いで、1/q dq/dtも低く、これは低心拍出量を意味する。そうでなければ、低い1/A dA/dtについて、1/v dv/dtが高い場合、したがって、1/q dq/dtも高く、これは、Δpは低くはないが、C、すなわち血管コンプライアンスが低いことを意味する。 However, according to the compliance relationship, measuring a low 1/A dA/dt can also mean a low Δp. Using relationship (4), we can further conclude that a low Δp is equivalent to a low:

Clearly, measuring 1/v dv/dt can alleviate the ambiguity as follows. That is, if 1/v dv/dt is low, then 1/q dq/dt is also low, which means low cardiac output. Otherwise, for low 1/A dA/dt, if 1/v dv/dt is high, and therefore 1/q dq/dt is also high, this means that Δp is not low, but C, ie vascular compliance means low.

Therefore, measuring and combining 1/v dv/dt and 1/A dA/dt makes it possible to distinguish between low cardiac output (and low peripheral perfusion) and low vascular compliance. Changes in vascular compliance can be detected and whether this is due to reduced cardiac output can be assessed.

In the following, methods are described to estimate vascular mechanical parameters and thus distinguish low cardiac output or vascular compliance from low peripheral perfusion. Therefore, it is necessary to estimate 1/v dv/dt in addition to 1/A dA/dt from the PPG signal.

Speckle imaging, such as laser speckle imaging (LSI), is used in one embodiment to measure blood flow velocity. When light, such as laser light, illuminates a diffusive medium, the interference creates a random pattern known as speckle. If there is motion in the medium, this will result in motion blur in the speckle pattern. Motion blur can be used to extract information about motion. This is done, for example, by imaging a speckle pattern. The velocity distribution is obtained by analyzing the variation of speckle contrast.

Similar to the PPG signal, the speckle signal can also be decomposed into an AC component reflecting the modulation of blood flow velocity and a DC component reflecting blood flow. Therefore, the combination of the two signals can distinguish poor peripheral perfusion or low vascular compliance from low cardiac output. Low blood volume fluctuations that can be observed in PPG signals due to small AC/DC components or small 1/A dA/dt correspond to:
i) small response of blood velocity modulation depth 1/v dv/dt (correlated to speckle (LSI) AC/DC signal) when cardiac output is low, or ii) non-compliant vessels (stiffening , indicating concentration), there is a large response in the blood velocity 1/v dv/dt (which is correlated to the modulation depth of the LSI signal). A large response in blood flow velocity indicates high cardiac output.

An example of a PPG signal and a speckle signal (as one embodiment of a flow signal) for different situations is illustrated in FIG. FIG. 5A shows a situation where the modulation in the PPG signal and the modulation in the speckle signal (LSI signal) are low (small) indicating low cardiac output. In addition to low cardiac output, vascular compliance may also be low. This situation can be considered indicative of maladaptive hypovolemia. FIG. 5B shows a situation where the modulation on the PPG signal is low and the modulation on the speckle signal (LSI signal) is high (large) indicating low vascular compliance. In other words, the situation illustrated in FIG. 5B can indicate (simply) low vascular compliance but sufficient cardiac output. This situation can be considered indicative of well-compensated hypovolemia.

Given the considerations discussed above regarding vascular response, the following inferences may apply and can be summarized in the table below:

Vascular compliance is low when the speckle signal indicates high flow velocities and the PPG signal measures relatively low blood volume fluctuations. In other words, blood vessels are not responding well to increased blood flow. As a result, similar conclusions can be drawn. Normal or high vascular compliance should prevent high blood flow velocity (measurable by speckle signal) by increasing blood volume (PPG signal).

Pの増加は血管収縮の増加を示し、Pの減少は心拍出量の減少を示す。 Based on the inferences from the table above, we can define the following compliance measures:

An increase in P indicates an increase in vasoconstriction and a decrease in P indicates a decrease in cardiac output.

In summary, the proposed idea combines two measurement methods: PPG imaging and flow signal evaluation (eg speckle imaging (eg LSI) or laser Doppler imaging). This may be based on single camera measurements (which are non-contact) or a combination of camera and contact measurements. It generally does not require visible light. From those measurements a PPG signal and a flow signal are derived and from these signals e.g. based on the functional relationship between the compliance measurement P, the PPG signal amplitude and the flow signal amplitude (e.g. ), or based on a tabular relation (eg, based on a lookup table: LUT) to obtain desired information about peripheral arterial perfusion.

In addition to distinguishing between low cardiac output and low vascular compliance, activity, posture, biometrics and/or vital signs can be determined and monitored, especially from the acquired second detection data. This information can be used in addition to decisions regarding arterial perfusion.

Another advantage of the proposed solution is that, since it is based on local area measurements, compliance in easily accessible areas such as the face, arms, etc. can be conveniently measured. As mentioned above, the method is preferably designed for remote measurement, but can also be adapted for contact.

Furthermore, light-based solutions are proposed so that measurements can be made in any of the invisible parts of the spectrum, allowing measurements in the dark and/or visible range.

A flow chart of one embodiment of a method 100 in accordance with the present invention is illustrated in FIG. In a first step S10, first detection data of a tissue region of a subject are obtained. In a second step S12, second detection data of the skin area of the subject are obtained. In a third step S14 a PPG signal is derived from the first detected data. In a fourth step S16 (which may be performed before or at the same time as the third step S14), flow signals are derived from the second sensed data. In a fifth step S18, the PPG signal and the flow signal are evaluated to obtain information on peripheral arterial perfusion. Based on the combined evaluation of the PPG signal and the blood flow signal, a state of low vascular compliance and/or a state of low cardiac output can be determined.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary, and not restrictive, and the invention may be practiced in accordance with the disclosed embodiments. Not limited. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, this disclosure, and the appended claims.

In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The computer program may be stored/distributed on any suitable non-transitory medium, such as optical storage media or solid-state media supplied with or as part of other hardware, Internet or other wired or wireless It may also be distributed in other ways, such as via a telecommunications system.

Any reference signs in the claims should not be construed as limiting the scope.

Claims (16)

In a processing device for use in monitoring peripheral arterial perfusion of a subject:
an input for receiving first detected data of a tissue region of a subject and for receiving second detected data of a skin region of a subject, wherein the first detected data is reflected from tissue of the subject; and/or obtained over time by detecting radiation transmitted through tissue of the subject, wherein the second detected data is obtained from the skin area in response to coherent light emitted toward the skin area. the input obtained over time by detecting received radiation;
a PPG unit for deriving a photoplethysmography (PPG) signal from said first detected data;
a flow unit for deriving from the second sensed data a flow signal indicative of the flow of light scattering particles within the skin area;
an evaluation unit for evaluating the PPG signal and the flow signal to obtain information about the peripheral arterial perfusion, wherein the evaluation unit determines, based on a combined evaluation of the PPG signal and the flow signal, low vascular compliance; an assessment unit adapted to distinguish between a condition of low cardiac output and a condition of low cardiac output;
A processing device, comprising: said flow unit is configured to derive said flow signal based on laser Doppler and/or laser speckle techniques;
A processing device according to claim 1 . the evaluation unit is configured to evaluate a speckle pattern represented by the flow signal;
A processing device according to claim 1 . wherein the evaluation unit is configured to evaluate motion blur by detecting speckle contrast variations;
4. A processing device according to claim 3. The evaluation unit is configured to evaluate the PPG ratio of the AC component to the DC component of the PPG signal and the speckle ratio of the AC component to the DC component of the flow signal.
A processing device according to claim 1 . The evaluation unit determines a status of well-compensated hypovolemia of the subject if the speckle ratio exceeds a first speckle threshold and the PPG ratio is below a first PPG threshold; is less than a second speckle threshold and the PPG ratio is less than the first PPG threshold, determining the status of maladaptive hypovolemia of the subject.
6. A processing device according to claim 5. The evaluation unit comprises:

configured to evaluate a compliance measure P indicative of the ratio of said PPG ratio to said speckle ratio, said speckle ratio being the ratio of the AC component to the DC component of said flow signal, given by said PPG ratio is the ratio of the AC component to the DC component of the PPG signal;
6. A processing device according to claim 5. the input unit is configured to obtain first detection data obtained in response to artificial illumination of the tissue with a predetermined radiation;
A processing device according to claim 1 . further configured to use the second sensed data as the first sensed data;
A processing device according to claim 1 . A system for monitoring peripheral arterial perfusion, the system comprising:
A detector for obtaining first detected data of a tissue region of a subject and obtaining second detected data of a skin region of a subject, the first detected data being reflected from tissue of the subject. and/or obtained over time by detecting radiation transmitted through tissue of the subject, wherein the second detection data comprises a series of images of the skin area obtained over time. vessel and;
a processing device of claim 1 for monitoring peripheral arterial perfusion based on the acquired first and second sensing data;
A system comprising: an illumination unit for artificial illumination of said tissue with predetermined radiation;
11. The system of claim 10, further comprising: the illumination unit comprises a coherent light source for emitting coherent light to illuminate the skin area;
12. The system of claim 11. A method of operating a processing device for use in monitoring peripheral arterial perfusion, the method comprising:
the input of the processing device receiving first detected data of a tissue region of a subject, the first detected data being reflected from and/or through tissue of the subject; data obtained over time by detecting transmitted radiation;
said input receiving second detection data of a skin area of a subject, said second detection data being received from said skin area in response to coherent light emitted towards said skin area. data obtained over time by detecting radiation;
a PPG unit of said processing device deriving a photoplethysmography (PPG) signal from said first detected data;
a flow unit of said processing device deriving from said second detection data a flow signal indicative of the flow of light scattering particles within said skin area;
An evaluation unit of the processing device evaluates the PPG signal and the flow signal to obtain information about peripheral arterial perfusion, and based on a combined evaluation of the PPG signal and the flow signal, a low vascular compliance state and a low heart rate. distinguishing between output states;
method of operation, including 14. A computer program comprising program code means for causing the computer to perform the steps of the method of operation according to claim 13, when the computer program is run on a computer. 12. The processing device of claim 8 or the system of claim 11, wherein the predetermined radiation is visible light or infrared light. 13. The system of Claim 12, wherein the coherent light source is a laser device for emitting a laser beam.

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